A mini-excavator (i.e., a hydraulic excavator having an operating mass of less than 6 tons) that is one example of a construction machine is generally equipped with a lower track structure, an upper swing structure swingably provided on the lower track structure, and an articulated work device provided elevatably relative to the upper swing structure and including a boom, an arm and a bucket. This mini-excavator is equipped with, for example, a hydraulic pump, a plurality of hydraulic actuators (in detail, e.g., a boom hydraulic cylinder, an arm hydraulic cylinder and a bucket hydraulic cylinder, etc.), a plurality of directional control valves which respectively control the flow of pressurized fluid from the hydraulic pump to the plurality of hydraulic actuators, and operating means (in detail, e.g., a plurality of operating devices each of which outputs pilot pressure corresponding to the position of operation of each control lever) which respectively operate the plurality of directional control valves.
There has recently been proposed an electric motor-driven mini-excavator equipped with an electric motor (motor-generator) instead of an engine as a drive source of the hydraulic pump because it has the advantage of greatly reducing even noise and vibrations without discharging exhaust emissions (refer to, for example, Patent Document 1).